In the field of automation, programmable logic controllers (PLCs) are widely used for controlling or regulating a machine or a system, wherein the PLC is connected to the machine or system particularly by means of sensors and actuators. The PLC can be connected directly to the sensors and actuators via inputs and outputs, or via a communication network such as a bus system, for example. The process control is performed by means of an application program executed by the PLC, wherein an operating program of the PLC, which is also called firmware, ensures that the application has access to updated process data.
Application programs for programmable logic controllers are typically written using one of the programming languages defined in the IEC61131-3 standard. When the control program is written pursuant to IEC61131-3 in an engineering system, program variables are assigned to process data objects via which access to input and output data, and therefore to signals from sensors, as well as control signals for actuators, is made possible. After the control program is written, with assignment of the program variables, the PLC-specific code is generated by compiling, and is transmitted to the target system in question.
For the assignment of the program variables to the process data to be changed, the control program in the engineering system must be accordingly modified and re-compiled in order to generate accordingly modified PLC-specific code. For instance, to assign the I/O channel of another module to a program variable, the control project must be adapted with an engineering tool and reloaded into the PLC. This may be inflexible and difficult in certain system startup scenarios.